1. Field of the Invention
The present invention relates to bearing brackets for Venetian blinds and in particular to a bearing bracket for outer wall Venetian blinds for lowering and lifting of the Venetian blind laths and their adjustment to three predetermined positions of adjustment.
2. Description of the Prior Art
Outer-wall Venetian blinds are normally mounted on the outer surface of buildings to be lowered as a sun-shade in front of the window of the buildings. Many Venetian blind units are required in order to cover all the windows of a building on one outer wall. For aesthetic reasons it has become desirable to enable the laths of all these Venetian blind units to assume the same positions of adjustment and it has accordingly become normal to predetermine three positions of adjustment or inclination, namely one in which the Venetian blind is fully open, one in which it is fully closed and an intermediate position. Irrespectively of whether the lifting, lowering, and adjustment of the Venetian blinds is performed manually or by some control equipment, e.g. electrically, it is preferred that all the blind units on one and the same outer wall assume the same positions of adjustment.
As examples of prior-art constructions for achieving the above-mentioned aims reference may be made to the contents of Swedish specification No. 74 14482-5 and Swedish published specification No. 76 10441-3. However, these constructions are extremely complicated and bulky whereby their use has been limited and they are sensitive to malfunction due to contaminants. In particular, there is a tendency for dirt and other foreign matter to penetrate the housing and interfer with the operation of the gear mechanism.
In order to keep costs at a minimum and reliability at a maximum, all the parts combined in a Venetian blind should be as simple and few as possible. For this reason it is attempted to use the same source of operation for both lifting, lowering and inclination, and in order to achieve this, attempts have been made to find some sort of coupling between the mechanism responsible for lifting and lowering and the mechanism responsible for the inclination or skewing position of the laths.
As a result, sophisticated bearing brackets have been obtained belonging to the type appearing from the abovementioned publications and comprising both lifting and turning rolls with a coupling inserted between them.
It is a requirement in connection with outer-wall Venetian blinds that the skewing positions of the laths should be maintained even when the blinds are exposed to squall winds, rain, snow and other severe weather conditions. In addition, it is a strong desideratum that during lifting and lowering of the blinds the laths are so skewed that light is permitted to enter and that the bearing brackets do not make any considerable noise during operation of the blinds.
In order to obtain a reliable wind securing the intention has primarily been directed to a use of pawls and ratchet wheel which give a safe locking engagement between the parts as result. However, such a construction shows the disadvantage that when the disconnected pawl is sliding over the teeth on the ratchet wheel there is generated a ratching noise, this noise being stronger and stronger in relation to the increasing force by which the pawls are biased against the ratchet wheel. A strong bias is also generating a heavy wearing.
In order to reduce the noise and the wearing one is trying to keep the bias of the pawls against the ratchet wheel as low as possible and in the known constructions only the dead weight of the pawls is used as the biasing force. However, normally the bearing brackets are mounted outdoors and together with the winds dust and other contaiminants are, accordingly, easily whirling into the brackets and the result thereof is the fact that the pawls jam and do not turn to their locking positions.
As there might be hundreds of bearing brackets on one and the same outer wall it is realized that the noise from the operation of the Venetian blinds can be troublesome as all the Venetian blinds are operated simultaneously and in order to reduce such a noise it is a desideratum to get as quiet bearing brackets as possible. If the bearing brackets then are of the type including pawls the cleaning of hundreds of such brackets for safe function will be an extensive and expensive work.